Oroville Dam spillway work to continue, flows go to 0

An aerial view of the Lake Oroville flood control spillway as water rushes into the diversion pool from a ravine created by the spillway incident. The California Department of Water Resources continues to release water from Lake Oroville at an outflow of

Photo Credit: Florence Low / California Department of Water Resources

by Department of Water Resources
3-27-2017

From Maven's Notebook: This morning, the Department of Water Resources held a press conference about the continuing operations at Oroville Dam and along the Feather River. Here’s what they had to say.

ACTING DWR DIRECTOR BILL CROYLE
Bill Croyle began by expressing his appreciation for the local communities of the city of Oroville, Butte County, and those downstream who have been participating in outreach activities. “Being engaged asking those questions and participating in these kinds of events and activities is super important for all of us to learn from what has happened here in Oroville, for in the end, we’ll have a safer dam and safer communities and be more prepared for almost any emergency that might come our way.”

He then ran down the numbers. The current lake elevation is a little less than 836.8’. Inflow is fluctuating due to the diurnal effects of day and night; right now inflow is 23,000cfs. The spillway flow is at 40,000 cfs. The Hyatt Power Plant is currently at 0 cfs; the tailrace elevation is 232.8’. Total river flow down the Feather River is still at 40,000 cfs.

Weather is expected to be favorable over the coming days; a little bit of weather is anticipated up canyon on Thursday and Friday, but not a lot. Looking ten days out for the Feather River, a small event that is forecasted starting on April 4, through the 6 or 7th.

There is plenty of water and snow in the watershed. Northern California is approaching and likely will soon exceed the second wettest year on record that goes back 100 years. We are not quite there yet but we don’t need too much more rain. Since the water year goes through October 1st, there is still plenty of time remaining to break that second wettest year on record, if not the wettest year on record.

Forecasted inflows for the next week are 17,000 cfs, increasing to 27,000 cfs later in the week. “We will see higher flows during parts of the days and then lower flows. Especially there’s a lot of other smaller reservoirs up stream, we have other reservoirs that are now spilling. Lake Davis was in the paper, Frenchman … this is the time of year, with the kind of snowpack and the weather we’ve had, we’re going to see those kinds of spills and those are being factored into the inflows and then resulting operations here at Oroville Dam.”

Flow was turned back on the spillway on March 17. They began at 50,000 cfs and then dropped back to 40,000 to minimize erosion within the channel to the south side of what’s left of the spillway, and backwater concerns on the Hyatt Power House. Because of the backwater effect, they backed off on those releases and then went to 0 flow to do preventative maintenance to get the plant ready to go full operation.

“We’re going to start reducing the flow from 40,000 to 0 starting at noon today. The process to step down has been revised and tweaked. We had a lot of consultation with our downstream water agencies, the flood operations center, local levee maintaining agencies, and our fish resource agencies to make sure that all the concerns that everyone might have are factored into our revised plan. This will take place for about 6 hours, and as we step in here in about four or five hours, we’ll see Hyatt Power Plant come back up to full operation. We will continue to manage our flows during different time steps, so about when sometime on Wednesday morning, at least the plan is to be at about 13,000 more or less in the Feather River downstream.”

“Our step today is as we start at 40,000, we’ll go to 35,000, hold for two hours; step again down to 30,000, hold for two hours; and then quickly step down from 0 to that. At the same time, once we get to 30,000 and watch the step over 45 minutes down to 0, we’ll be pulling up both the Hyatt Power House and making additional releases from the Thermalito Afterbay.”

“It’s a fairly complicated process, and fortunately we have a lot of different pools of water that we can draw from, so that’s what we have, part of our emergency response team is spread throughout the region so that we can watch, turn those dials, give those monitoring and make sure the system is acting as we’ve planned.”

“Once we go through this process, again we’ll be limited to the operation of the Hyatt Power House. Right now we have five turbines at our disposal. We’ll maximize those at 12,900 like we did for quite awhile. We also have some other things going on. We want to make sure we’re operating that plant for maximum efficiency, maintenance, etc. because we want that plant to work hard all summer, so over the next number of weeks, we’ll make sure that we’re doing that maintenance, and so we may do adjustments for either plant reasons or for the backwater concerns. As we come off the spillway, we should see far less concern with the backwater and we’ll see how that works here in the next 3 of 4 days.”

“While we’re off at 0 flow off that spillway, there’s a number of planned activities. We’re going to get back on the major activity of getting rid of the dredge material that’s down in the diversion pool. We’ll be rebuilding some of the roads to access that area, especially the area on the south that eroded away with this high flow event. We’re going to rebuild that access road so we can have the remove dredge material going both ways to the north and to the south. We’ll do a little bit more armoring at the base of the spillway again to help facilitate that dredging and removal of that material to those spoil sites.”

“We’ll go through a process here later today and tomorrow to tag out the gates, make sure when its safe and get it clear to get back in the emergency spillway. We’ll do what we did last time, which is inspect 100% of that upper spillway and start any repairs that might be needed. Quite a bit of work has been done, but again they’ll go back in, check for any additional work and anything that may have happened, that includes any of that shotcrete that we put in off the very end of the spillway and underneath, they’ll go and look at that, inspect how that held up, and then if there’s things that they feel they want to do or need to do, then they’ll go ahead and plan that out for this next week.”

“We’re going to go back to sealing any and all joints, make repairs where its fallen or some of the concrete pieces come up because of the water flowing off the top of the deck. As for additional dredging, right now we’re sitting still at about 1.26 million cubic yards of material, and again the number of 1.7 million cubic cards total still stands. When we pull this down, we’ll reassess to see how much additional material that we may have to add on to that.”

They will also be working to stabilize the slopes to make it safer for the emergency response teams to monitor the stability of the spillway and get ready for the next spill. “Some of that will also help us have a better idea how we access the area for the ultimate recovery of this spillway, and the emergency recovery efforts planned later this year.”

Drill rigs have mobilized on site to drill holes to collect geologic information. “One of the things we’re continuing to evaluate is how many holes that we want to put in the spillway itself. That’s part of our discussion in the coming days so as we put that drilling equipment back in the spillway, then we can get on with some of that geologic assessments. That’s obviously important for gathering information to validate the preliminary designs that are being developed right now with this multiagency regulatory independent board process.”

The work on the emergency spillway work is complete or near complete. Then the recovery team will b back in to assess the geologic structure and alternatives to bring that spillway back into the design criteria.

“As soon as an emergency incident starts, emergency managers need to start the recovery activity, and so that started about the same time this event happened back on February 7. They are becoming more active. Some of the trailers showing up on the field office site are for those recovery teams to come together, transition from response into recovery. We’re collecting that information.”

“There’s a number of activities that are being planned, and so those activities are being implemented now. One of which, as I understand this morning, the contract was let for the construction, the alignment, the improvements for the Burmer Road; again that’s going to be a major access point for a lot of the construction equipment needed to access the spillway from the north. There’s a rock crusher on site. The rock crusher is going through the process of crushing rock that is available here on site and testing it so we can see if it meets the specs for ultimate reconstruction of the spillway. There’s a lot of fencing for public safety … There’s a concrete batch plant that’s in the process of being acquired to mobilize that equipment. Even though we don’t’ have the design done and approved, there’s a number of things we need to do now to be sure we’re prepared for when it is time to start the physical reconstruction, all the staging is done, all the materials are on site, the coordination between a lot of different entities and contractors needs to take place.”

“We will, if I have anything to do with it, have a spillway to use November 1st. Whether that’s a permanent or a temporary structure is yet to be decided. Part of that comes back to the alternatives that are being vetted out through not only the department but our regulatory agencies, our independent board of consultants, and ultimately we’re briefing the Governor, the water contractors, etc. to make sure we are doing everything we can to implement a corrective action before wet season next year. … We expect to have a 60% design vetted through the process later this week or very early next week. That will be what we talk about next time we get together, what that design looks like and what the contingency plans for if a particular design is executed and we run into a road block is what are those other things we’re going to do to ensure that we have a safe and usable spillway and an emergency spillway for this next flood season.”

DEPARTMENT OF FISH AND WILDLIFE
An official for the Department of Fish and Wildlife began with acknowledging the effort and coordination between DFW and DWR. “They worked really hard to help us save 9 million fish with virtually no losses whatsoever so for the state’s anglers, which is our concern. It was just a tremendous effort.”

Last Monday, they released the first million spring run chinook salmon; the next million fish are being tagged with a PIT tag so in three years they’ll know how successful they were during this incident. The Oroville hatchery is a critically important hatchery that raises more than 50% of the state’s fall-run chinook salmon. There’s an additional 4 million fall run chinook salmon at the annex hatchery which will be released when they are of appropriate size and the water conditions are right.

There is a joint DWR-DFW effort to rescue fish and assess the riverbank; that work will continue this week. The Feather River hatchery remains closed until further notice.